1. Field of the Invention
The present invention generally relates to illuminating devices and, more specifically, to light pipes and light guides. The assembly according to the present invention will find utility in vehicle lighting systems, as well as in a variety of non-automotive illumination applications.
2. Description of Related Art
Light pipes and light guides are used in exterior vehicle lighting applications and a variety of other applications, such as interior vehicle lighting applications, interior and exterior architectural lighting, and backlighting for liquid crystal display screens. A plurality of prisms, prismatic cuts, steps, or angled surfaces are formed within the light guide, which are intended to reflect light out of a side of the light guide. Typically, the angled surfaces are disposed on one face of the light guide and a light-emitting face is disposed opposite the angled surfaces. Light rays entering an end of the light guide are incident at the surface of the angled surfaces, and are reflected back through the cross-section of the light guide so as to exit the light guide through the light-emitting face, which is disposed opposite the face having the angled surfaces, as noted above.
Light guides can be oriented vertically or horizontally. The angled surfaces are typically designed with large angles of inclusion, such as 45°, so that when a light beam traveling within the light guide hits a particular angled surface, the light beam is totally internally reflected and exits the light guide through the surface opposite the angled surface.
With reference to FIGS. 1 and 2, a light guide or light manifold 20 is illustrated. A collimated light source S is located at one end of the light manifold 20 and generates light rays 22. The light rays 22 enter a light-receiving face 24 of the manifold 20. The back side 26 of the light manifold 20 includes gradual steps 28, generally angled at 45 degrees to the direction of the incoming light (i.e., with reference to FIG. 2, α is approximately 45°). The angled steps 28 generally reflect the light rays 22 via total internal reflection (TIR) back through the light manifold 20 and out the light-emitting face 30.
The resulting shape of the light manifold 20 is roughly triangular—thick near the light source S and thin at the distal end 32. For a given length, the size and spacing of the 45-degree steps 28 will determine the maximum thickness of the light manifold 20. Customer styling is moving toward a uniform lit appearance, which means the pitch P between steps 28 is preferably small (for example, on the order of about 1-2.5 mm). Thus, for a long or tall lamp, the thickness T of the light manifold 20 is quite large near the light-receiving face 24. In some cases, the resulting mold cycle times become so great as to be impractical.
One solution has been to change the optical mechanism from TIR to simple reflection by using a metalized reflector having a profile substantially similar to the back surface 26 of the light manifold 20. However, the resulting appearance (both lit and unlit) of the lamp has not been adequate to satisfy customer requirements. Further, in some cases, the signal lamp is in close proximity to an electronic device on the vehicle, such as an antenna, and a metalized reflector may cause electromagnetic interference therewith.
Therefore, there remains a need for a light guide or light manifold which uses TIR principles to reflect light, while remaining within an acceptable thickness for purposes of manufacturing and packaging.